I occasionally get email delivery failures saying that our IP address is on “one or more DNS blacklists” - is there some way to remedy this? We’re not spammers.
You need to find out which one(s) and then visit the site of the blacklist and follow their instructions.
MX Toolbox will tell you what blacklists you’re on. Some blacklists are totally bullshit, but I can’t remember which ones off the top of my head. The more convoluted it is to get off, or the more it COSTS to get off, the more likely they are bullshit.
To expand, there are various things like some part of your mail server being unsecured or out of date that will make some of the more aggressive blacklist services list your IP. They aren’t necessarily saying your server has sent any spam, just that it has the potential to, and that makes you a “bad net citizen.” Also not having a proper opt-in and opt-out system on your mailing lists can get you blacklisted. Or it could be simply too many forgetful/lazy/spiteful recipients reporting your e-mail as spam.
Keep in mind that the blacklist maintainers, whether their criteria are fair or not, aren’t blocking any email. They just maintain a list that receiving e-mail servers can optionally and deliberately use to filter incoming email.